The semiconductor industry employs ion implantation in the manufacture and processing of very large scale integrated circuits. Ion implantation is a process by which dopants are added to a workpiece, such as a semiconductor wafer by impacting accelerated charged atoms or molecules (positive or negative ions) against semiconductor substrates. One of the objectives of ion implantation is to introduce a desired atomic species into the target material, the semiconductor wafer or workpiece.
Hot cathode DC arc ion sources have been the standard in semiconductor ion implantation. These sources have an internal cathode that is negatively biased with respect to the ion source body walls. Electrons are accelerated away from the cathode toward the walls of the ion source, ionizing gas molecules and thereby creating a plasma. The body of the ion source is typically supported inside of a vacuum system and therefore the source body is thermally isolated from the outside. Gases within the source body build up on the walls of the ion source if the source and/or source walls are not sufficiently hot. For example, if arsine (an arsenic hydrogen compound) is used, arsenic (As), that did not ionize, can plate out on the source walls as a contaminant. If the ion source body does not reach a high enough temperature, the Arsenic will remain on the walls and can contaminate future implantation when the system is changed over to a new gas, for example, phosphine (PH3). However, ion sources for semiconductor ion implantation are generally operated at temperatures of 300-600 degrees Celsius (572-1112 degrees Fahrenheit) in order to avoid deposition on the ion source surfaces.
Standard RF source design requires that the ion source wall temperature be in the range of approximately 20-100 degrees Celsius (68-212 degrees Fahrenheit). This incompatibility in temperature requirements has prevented the widespread use of RF sources in the semiconductor ion implant industry.
In addition, current arc discharge DC ion sources can only run a few hundred hours or less before having to perform maintenance on the ion source. The cathode is worn out by the constant bombardment of ions and therefore has to be replaced.
In view of the above problems associated with current arc discharge DC ion sources and RF ion beam sources with regard to semiconductor manufacture and processing, it would therefore be desirable to have a system and method which mitigates such issues. Thus, there exists a need for an improved system and method for ion sources used in semiconductor implantation.